Depth gauge



FIG. 1 is a front elevational view of a depth gauge showing my new design;

FIG. 2 is a top plan view thereof;

FIG. 3 is a bottom plan view thereof;

FIG. 4 is a rear elevational view;

FIG. 5 is a right side elevational view;

FIG. 6 is a left side elevational view. 

The ornamental design for a depth gauge, as shown. 